It is known to pack tea or other goods into bags which are infused with hot water for use. These bags typically are made up of a first ply of a porous material composed of is natural fibers and of a second ply composed of hot-melting polymeric fibers such as for example PP, PE or various interpolymers. This second ply serves to close the bag by heatsealing on high-speed packing machines.
This bag material can be produced in known manner by a wet-laid process on a paper machine, by a dry-laid process on a webbing machine or by a melt-blown process by laydown of polymeric fibers on a support layer.
The basis weight of the first ply of the material is generally in the range 8-40 g/m2 and preferably in the range 10-20 g/m2, the basis weight of the second polymeric fibrous ply is in the range 1-15 g/m2 and preferably in the range 1.5-10 g/m2.
It is known that used filter bags are disposed of on a compost heap or via the biowaste bin. After a certain period, which depends on further parameters such as temperature, moisture, microorganisms, etc, the natural fiber component of the filter bag will have disintegrated and become biodegraded, whereas the thermoplastic polymeric fibrous network remains intact and compromises the quality of the compost.
It is not practicable to separate the natural fiber component from the thermoplastic polymeric component; that is, the used filter bag ought to be put into the nonrecyclable waste (Gray Bin).
EP-A-0 380 127 describes a heatsealable paper for tea bags which has a basis weight of 10-15 g/m2 and which for heatsealing has been provided with polymers such as PP, PE or an interpolymer and therefore is not biodegradable.
is EP-A-0 656 224 describes a filter material especially for producing tea bags and coffee bags or filters having a basis weight between 8 and 40 g/m2, wherein the heatsealable ply consists of polymeric fibers, preferably of polypropylene or polyethylene, which is laid down in the soft state onto the first ply, which consists of natural fibers.
JP-A-2001-131826 describes the production of biodegradable monofilaments from poly L lactide and the subsequent production therefrom of wholly synthetic woven tea bags by a dry-laid process.
The German patent application DE-A 21 47 321 describes a thermoplastic heatsealable composition which consists of a polyolefin powder (polyethylene or polypropylene) which is embedded in a carrier matrix of vinyl chloride-vinyl acetate copolymer. This material is likewise used for conferring heatsealability on fiber material produced by a papermaking process.
DE-A-197 19 807 describes a biodegradable heatsealable filter material of at least one ply of natural fibers and at least one second ply of heatsealable synthetic material which is biodegradable. This filter material is obtained by first applying an aqueous suspension of natural fibers to a paper machine wire and then depositing the heatsealable biodegradable polymeric fibers on the natural fiber layer in such a way that they are able to partly penetrate through the natural fiber layer.
A tea filter bag, for example, produced from this filter material has a high particle retention potential. However, this is bought at the expense of reduced air permeability. Yet, high air permeability coupled with good particle retention is the ultimate objective for any good filter material.
Prior art filter materials thus suffer from at least one of the following disadvantages:    1. The used filter materials such as for example tea bags, coffee bags or else other filters are frequently disposed of on a compost heap or in the biowaste bin. After a certain period, which depends on further parameters such as temperature, moisture, microorganisms, etc, the natural fiber component of the filter will have disintegrated and become biodegraded, whereas the thermoplastic polymeric fibrous network composed of polymeric fibers which do not biodegrade completely remains intact and is compromises the quality of the compost.    And/or    2. The use of fully biodegradable polymeric materials known by prior art for tea bags and similar filter papers leads to the heatseal seams formed on a tea bag not withstanding a temperature of about 90-100° C.
This is because the production of heatsealed filled tea bags on high-speed packing machines occurs at a cycle time of about 1 000 bags per minute.
So-called heatsealing rolls generally seal the bag at a temperature of 150-230° C. in a cycle time of less than 1 second. In the course of these short cycle times, the heatsealing material has to melt, adhere together and immediately resolidify and crystallize in order that, in further transportation, the bag is already resealed and no contents may escape.
As mentioned above, however, prior art materials do not meet the requirements of this operation.